Biopolymer and isocyanate based binder and composite materials

ABSTRACT

A binder comprising isocyanate droplets in water, wherein the isocyanate droplets have an average droplet size of 500 microns or less, and the isocyanate droplets have shells comprising a biopolymer or a reaction product of a biopolymer and isocyanate. The biopolymer may be a biopolymer nanoparticle or cooked and chemically modified starch. Optionally, the binder may also include urea. The substrate for the binder may be wood, another lignocellulosic material, or synthetic or natural fibers. In particular examples, the binder is used to make no added formaldehyde wood composites including particle board and MDF.

RELATED APPLICATIONS

This patent claims the benefit of U.S. provisional application62/096,260, filed on Dec. 23, 2014, which is incorporated herein byreference.

FIELD

This specification relates to binders or thermosetting resins and tocomposite materials including a binder and wood, other lignocellulosicmaterials, or synthetic or natural fibers.

BACKGROUND

Composite wood products include, for example, particle board, mediumdensity fiberboard, oriented strand board (OSB), plywood and laminatedveneer lumber (LVL). Many composite wood products are conventionallymade with formaldehyde-based resins. However, concerns over excessformaldehyde emissions have encouraged the creation of “no addedformaldehyde” (NAF) resins. Replacement resins should meet relevantperformance requirements for the end product, such as bonding strengthand water resistance. However, replacement resins must also meet variousrequirements of the manufacturing process.

Isocyanate binders, such as polymeric methylene diphenyl diisocyanate(pMDI), have been used to make NAF wood composites such as particleboard or MDF. pMDI is used to make these products because, among otherattributes, it has a low viscosity (less than 500 cPs at 40° C.)suitable for spraying on sawdust or wood chips in blow lines orresonators resulting in finished boards with good water tolerance andmechanical properties. However, pMDI has some disadvantages. Forexample, pMDI can be absorbed by wood, so it does not always produce aneffective bond at the surface of the wood particle unless applied in anamount sufficient to provide good coverage despite the adsorption. SincepMDI is not miscible in water, it is typically used in a 100% activeliquid and coverage cannot be increased without increasing the amount ofpMDI used. Bond quality may also be reduced because isocyanate-basedbinders can start curing before the wood is pressed. Combining theamount of pMDI needed to overcome these difficulties with the unitvolume price of the raw material results in pMDI based products beingmore expensive than formaldehyde based products. pMDI also tends tobuild up on metal surfaces such as in press plates and processingequipment requiring release agents and regular process cleanup resultingin machine downtime. Machining wood products made with pMDI has thepotential to cause increased tool wear relative to products made withrelatively soft urea-formaldehyde (UF) based resins. Despite thesedisadvantages, pMDI is still one of the leading binders used for makingNAF particle board and MDF. The low viscosity of pMDI, whileadvantageous in sprayed applications, makes pMDI unsuitable for makingother composites, such as plywood or veneer, where higher viscositybinders are used.

U.S. Pat. No. 4,801,631 describes an aqueous dispersion containing about15 to 30% by weight of polyisocyanates, 10 to 15% cold water solublestarch and 14 to 25% of flour and the appropriate amount of water to addup to 100%. Exemplary dispersions had at least one hour of pot life anda viscosity of about 2000 centipoise (cP). The dispersions were spreadon wood veneers and cured. Samples made without the flour had similarviscosity but a pot life of less than 30 minutes.

U.S. Pat. No. 4,944,823 relates primarily to water free compositionscontaining an isocyanate and sugar or starch. However, in one example anaqueous composition was made by first blending 20% MDI with 80%industrial wheat flour for 5 minutes, letting the mixture react for 10minutes, and then mixing 100 grams of the blend with 150 grams of waterfor 5 minutes. The resulting binder was spread on veneers to makeplywood. This binder is described as a viscous mass with a relativelyshort shelf life.

INTRODUCTION

The following introduction is intended to introduce the reader to thedetailed description to follow, and not to limit or define any claimedinvention.

There has been a need in the art for no added formaldehyde binders, anda specific need for a means of extending or dispersing an isocyanatebinder, for many years. The '631 and '823 patents, for example, wereissued in 1989 and 1990 respectively. More recently, some modifiedisocyanates (called EMDI) have been developed that form emulsions inwater. These products help with the coverage issue described above, butonly by using a product that is even more expensive than pMDI and stillmade from petroleum. Efforts to mix pMDI with bio-based materials havenot yet, to the knowledge of the inventors, been commercialized. The twopatents described above suggest that biopolymer and pMDI based bindersare prone to having high viscosity and short pot life, which wouldprevent them from being used in industrial scale equipment for makingcommon wood composites such as particle board and MDF. In thisspecification, the inventors describe biopolymer and isocyanate mixturesthat have low and stable viscosity, and also sufficient strength andwater resistance to provide alternative no added formaldehyde binders.Without intending to be bound by theory, these properties are believedto result from forming an emulsion of small isocyanate dropletsstabilized by a biopolymer shell, while limiting the viscositycontributed by biopolymer in the continuous phase of the emulsion.Preferably, the shell comprises starch or a bio-urethane formed by thereaction of isocyanate and starch. Surprisingly, even though isocyanatesare generally immiscible in water, the most stable emulsions areproduced when the isocyanate is mixed into only a limited amount ofwater.

This specification describes a binder having an isocyanate, a biopolymerand water. The preferred biopolymer is a starch nanoparticle or a lowmolecular weight starch. The mass of isocyanate is preferably between50% and 150% of the mass of water. Optionally, the binder may alsoinclude urea.

In a process described in this specification, a biopolymer is dispersedin water, and then an isocyanate is added to the dispersion. Optionally,more water may be added to dilute the resulting emulsion.

An emulsion described in this specification comprises a plurality ofisocyanate droplets, each surrounded by a starch shell. The isocyanatedroplets preferably have an average size from 10 to 500 microns.Optionally, the emulsion may further comprise starch in solution orstarch hydrogel particles.

A binder as described herein may have a viscosity that is suitable forbeing applied on a substrate to make composite materials such asparticle board and MDF, for example a viscosity of 700 cPs or less at40° C. The binder may also be used to make other wood composites, orcomposites of other lignocellulosic materials, or synthetic or naturalfibers.

FIGURES

FIG. 1 is a graph showing the initial RVA viscosity-phase ratiorelationship for an example of a pMDI (“oil”) in water emulsion at 40°C. in the presence of biopolymer nanoparticles in the following weightratio sample composition (Biopolymer:Urea:pMDI:Water)=(21:4:75:watervaries).

FIG. 2: Light microscopy images of pMDI in water emulsions at differentpMDI:Water phase ratios (β) in the presence of biopolymer nanoparticlesin the following weight ratio sample composition(Biopolymer:Urea:pMDI:Water)=(21:4:75:water varies). Scale bar in allimages equals 100 μm.

FIG. 3: Light microscopy images and droplet size data for an emulsioncreated at a pMDI:Water phase ratio of 1.60 and later diluted to a phaseratio of 1.00, indicating that the viscosity of the emulsion can befurther reduced by dilution without material reduction in the particlesize. Scale bar indicates 100 μm.

FIG. 4: Evolution of RVA viscosity over time at 40° C. for pMDI in wateremulsions in the presence of biopolymer nanoparticles in the followingweight ratio sample composition(Biopolymer:Urea:pMDI:Water)=(21:4:75:75). Viscosity measured in a rapidvisco analyzer at 100 rpm.

DETAILED DESCRIPTION

Isocyanates useful as binders include, without limitation, toluenediisocyanate (TDI), hexamethylene diisocyanate (HDI), methylene diphenyldiisocyanate (MDI) and polymeric MDI (pMDI). Polymeric MDI typically isa mixture of MDI, containing about 30 to 80% w/w 4,4′-methylene diphenylisocyanate, with the remainder of the mixture comprised of highermolecular weight MDI oligomers and polymers. Isocyanates are generallynot miscible in water although some emulsifiable MDI formulations (EMDI)are commercially available and may be used as binders.

Biopolymers useful as binders include, for example, carbohydrates,preferably starch. Binders may be made with starch in various modifiedforms, such as regenerated starch particles, chemically modified starch(i.e. hydrolyzed starch) or thermally modified starch (i.e. dextrinizedstarch). Chemically or thermally modified starches that can be used asbinders without cooking are often referred to commercially as coldsoluble starches. Regenerated starch is starch that has been convertedto a thermoplastic melt phase (its native crystalline structure has beenessentially removed) and then reconfigured into a particle, for exampleby crosslinking. Regenerated starch of an appropriate particle size isan example of a biopolymer nanoparticle starch. They are readilywater-dispersible and do not require cooking. Preferred starches have atleast a portion of the starch with a molecular weight of 1,000,000 Da orless. More preferred starches have a molecular weight of less 100,000 Daor have been regenerated into nanoparticles.

The manufacture of biopolymer nanoparticles is described, for example,in International Publication Number WO 00/69916 and InternationalPublication Number WO 2008/022127. Other methods are known in the artfor making biopolymer nanoparticles. Even though the term “nanoparticle”usually refers to particles 100 nm and smaller, in this specification itis used to refer to particles that have an average particle size ofabout 1000 nm or less or that form a colloid in water.

In principle, any obiopolymer, and mixtures thereof, may be used to makebiopolymer nanoparticles. In particular, any starch, for example waxy ordent corn starch, potato starch, tapioca starch, dextrin, dextran,starch ester, starch ether, hydroxyethylated or hydroxypropylatedstarch, carboxymethyl starch (CMS), cationic or anionic starch, andmixtures thereof, may be used. In an exemplary method, the biopolymer isheated and mechanically processed with water, optionally a plasticizer,optionally a crosslinker, and optionally other additives. The heatingand mechanical processing may occur in an extruder, preferably aco-rotating twin screw extruder. The biopolymer, water and anyplasticizer are preferably added to the feed zone of an extruder. Theplasticizer may be a polyol such as glycerol. The crosslinker may be areversible crosslinker. In an intermediate or gelatinization zone of theextruder, located downstream of the feed zone, the temperature ismaintained between 60 and 200 degrees C., or between 100 and 140 degreesC. At least 100 J/g, or at least 250 J/g, of specific mechanical energyper gram of the biopolymer is applied in the intermediate zone. Thepressure in the intermediate zone may be between 5 and 150 bar. Acrosslinker, if any, may be added in a reaction zone that follows, oroverlaps with the end of the intermediate zone. When the biopolymer isstarch, the starch is substantially gelatinized (converted into athermoplastic melt phase) in the intermediate zone. Starch nanoparticlesprimarily form hydrogel particles when dispersed although some of thestarch may dissolve. The starch in at least a portion of thenanoparticle may have a molecular weight between about 700,000 and800,000 Da.

A biopolymer based binder may have various secondary components.Examples of secondary components include urea, melamine and citric acid,and/or another nitrogen heterocycle. Urea is a crosslinker but alsoscavenges formaldehyde. Melamine can make biopolymers less hydrophilic.In the case of biopolymer nanoparticles, one or more secondarycomponents may optionally be added during the nanoparticle formationprocess. A biopolymer based binder is preferably made up of 50% or more,more preferably 80% or more, by weight of biopolymer before isocyanateis added.

To make composite materials, a binder is mixed with a substrate andcured. Curing is typically triggered by heat applied to the binder andsubstrate mixture. The binder and substrate are often compressed duringcuring. Alternatively, a two part binder is cured by mixing two parts ofthe binder together to initiate a curing reaction, and then mixing thebinder with the substrate before the reaction is complete. These twomethods may also be combined.

Composite material substrates include, for example, wood products andfibers. Wood products include veneer, wood chips, wood flour andsawdust. Fibers include, without limitation, natural (such as hemp,jute, and sisal), synthetic fibers (such as nylon, polyester andpolypropylene) and mineral fibers (such as fiberglass and mineral wool).Composite wood products include, for example, particle board, mediumdensity fiberboard (MDF), high density fiberboard (HDF), oriented strandboard (OSB), plywood, laminated veneer lumber (LVL) and wood thermalinsulation.

A binder useful in making composite materials, among other potentialapplications, has an isocyanate, a biopolymer and water. The biopolymeris preferably a starch based biopolymer nanoparticle, or a modifiedstarch having a molecular weight of less than 1,000,000. It ispreferable for the starch to not have a crystalline structure. Forexample, a modified (i.e. cold soluble) starch may be cooked or left ina dispersed state for a period of hours or days before isocyanate isadded It is predicted that cooking starch, chemically (optionallyenzymatically) or thermally modified before or after cooking, to reduceits molecular weight and remove crystalline structures, may also beuseful whether the starch is cold water soluble or not.

The mass of isocyanate is preferably not more than 150%, or not morethan 130%, or not more than 110% of the mass of water in a binder whenit is applied to wood. However, the mass of isocyanate may be more than150% of the mass of water when the isocyanate is added to a biopolymerin water dispersion. The mass of isocyanate is preferably not less than50% of the mass of water, at least when the isocyanate is added to abiopolymer in water dispersion. The binder may be diluted further afterthe isocyanate is added to a biopolymer in water dispersion. The mass ofbiopolymer is preferably not more than 55% of the mass of water. Thecombined mass of the isocyanate and biopolymer is preferably not morethan 175% or 150% of the mass of water. The ratio of biopolymer toisocyanate may be between 80:20 and 15:85 while producing strength andwater resistance properties comparable to products made with ureaformaldehyde (UF) binder. Biopolymer to isocyanate ratios of 50:50 to15:85 are preferred if the product is to have properties comparable toproducts made with a pMDI binder. Biopolymer to isocyanate ratios of25:75 or more are more preferred. Optionally, the binder may alsoinclude urea.

In a process described in this specification, the biopolymer and waterare mixed, and the isocyanate is added to the mixture. Preferably, thebiopolymer and water form a stable dispersion before isocyanate isadded. The isocyanate may be added to the biopolymer and water mixturewith mixing by mechanical agitation and/or feeding both components intoan in-line static mixer. The isocyanate and biopolymer in waterpreferably form a relatively stable emulsion. Mixing the isocyanate intoa biopolymer in water dispersion enables the isocyanate to form anaqueous mixture, possibly an emulsion or other dispersion, wherein someof the biopolymer reacts with the isocyanate to form a shell aroundisocyanate droplets. The term “relatively stable” used above preferablyindicates sufficient emulsion stability so as not to significantly buildviscosity for an acceptable time at a specific temperature. In industryterms, the requirement in terms of stability is to ensure that there issufficient process “pot life” for the aqueous isocyanate emulsion. Formaking particle board of MDF, viscosity should be less than 700 cPs at40° C. for at least 15 minutes. However, a preferred binder has aviscosity of less than 500 cPS, or more preferably less than 300 cPs. Apreferred binder remains with low viscosity for 30 minutes or more,preferably 60 minutes or more.

Simply mixing an oily isocyanate, such as MDI or pMDI, into water doesnot result in the formation of a stable mixture or emulsion, but quicklyphase separates into separate oily and aqueous layers. Without intendingto be limited by theory, the isocyanate component and the biopolymercomponent are believed to react at the oil-water interface to form apolymeric (bio-urethane) protective layer that results in enhancedemulsion stability (process pot life). Once this layer has formed, theemulsion may be diluted without loss of stability. Certain biopolymerssuch as starches and biopolymer nanoparticles are particularly suitablefor producing a polymeric protective layer for enhanced emulsionstability. Alternatively, the biopolymer might cap the isocyanate groupsor act as a surfactant to stabilize the isocyanate emulsion. In the caseof biopolymer nanoparticles, there may be an effect such as a Pickeringstabilization The binder is preferably relatively stable at roomtemperature, without excessive loss of short term NCO functionality. Thebinder is ultimately thermosetting and, after heat curing, preferablyunder pressure, it has minimal water solubility.

A binder as described herein may be formulated with a viscosity that issuitable for being sprayed on a substrate to make a composite material,or otherwise applied as in a blow line or resinator to make particleboard or MDF. When sprayed, or otherwise applied to wood while makingparticle board or MDF, a binder preferably has a viscosity of 700 cPs orless, preferably 500 cPs or less, at 40° C. For veneer based products,such as plywood and LVL, the viscosity is preferably in the range ofabout 1500-5000 cPs. Viscosity is typically measured by Brookfieldviscometer using spindle 5 and 200 or 100 rpm. Alternatively, viscositycan be measured by RVA at 100 rpm. Viscosity results determined by thesetwo methods are generally comparable, although the viscosity measured byRVA may be lower. In cases where viscosity is measured at roomtemperature (15-25° C.), the viscosity at 40° C. is generally roughlyabout half, for example 40-60%, of the viscosity measured at roomtemperature.

The substrate may be wood, another lignocellulosic material, orsynthetic or natural fibers. In particular examples, the binder is usedto make wood composites including particle board and MDF. pMDI alone istypically sprayed on wood chips or sawdust at about 3 to 6 g pMDI per100 g wood, the higher application rates being used for exterior gradeproducts. The combined biopolymer-isocyanate binder may be, for example,applied at 5 to 12 g (including water) of binder per 100 g wood. Theincreased application rate allows for a better distribution of binder onthe wood and may be compatible with equipment used for sprayingformaldehyde based resins, which is typically applied at about 10 g ureaformaldehyde (UF) per 100 g of wood. The combined weight of thebiopolymer and isocyanate (without water) may be between 2% and 6% ofthe weight of the wood, preferably between 2% and 4% of the weight ofthe wood for interior grade products and between 4% and 6% for exteriorgrade products.

In general, hybrid binders as described herein have a biopolymercomponent and an isocyanate component. The biopolymer component ispreferably made from at least 50% starch feedstock on a dry weightbasis. Optionally, there may also be a second compound provided with thebiopolymer component. The second compound may comprise a crosslinkerand/or hydrophobizing agent, for example an amide or amine compound,such as urea, melamine and citric acid, and/or another nitrogenheterocycle, or other compound with amine functionality. Isocyanatesuseful as binders include, without limitation, TDI, HDI, MDI and pMDI.The preferred isocyanate compound may be, for example, pMDI. Thecomponents may be mixed together before being applied to the wood orother fibres to be bound, or the biopolymer component and secondcompound (if any) may be applied together while the isocyanate componentis applied separately. Preferably, the binder is an aqueous composition.Without being limited by theory, aqueous binders having low viscosityare believed to be oil-in-water emulsions. However, hybrid binders asdescribed herein may or may not be an emulsion or any other type ofdispersion.

A preferred binder is made by first extruding starch, for example waxycorn starch or a mixture of different starches, for example 10-30%potato starch and 70-90% waxy corn starch, along with water and,preferably, a plasticizer and/or a crosslinker to form biopolymernanoparticles. These nanoparticles are preferably dispersed in waterwith about 10-25 parts per 100 parts starch of a second compound such asurea. This dispersion may have a solids content of about 25 to 50%. Thedispersion is then mixed in a ratio between about 80:20 and 15:85 withan isocyanate, for example pMDI or a mixture of pMDI with anotherisocyanate, on a solids (biopolymer and any urea) to solids (isocyanate)mass basis. The binder may be diluted by adding more water after theisocyanate is added. The resulting binder has a low viscosity suitablefor being sprayed or otherwise applied on wood chips or mixed with woodfibers in a blow line or resonator used to make particle board or MDF.

The isocyanate binder is miscible in the biopolymer dispersion. Thisallows a lower amount of total isocyanate binder to be used withcomparable performance in the finished composite product relative tousing pMDI alone. Without intending to be limited by theory, theinventors also believe that the higher molecular weight of thebiopolymer component (relative to pMDI) may assist in reducingabsorption of the binder into the wood and thereby improve coverage orbinding strength of the binder, or add a degree of plasticity to thebinder which may thereby reduce wear in tools working on the finishedproduct, or both. In tests, it was discovered that the hybrid binder didnot accumulate on metal surfaces as much as pMDI alone and required lessrelease agent in the press.

The second compound is not required for miscibility. However, the secondcompound may help reduce the viscosity of the dispersion and/or mayimprove one or more qualities of the finished product. Urea inparticular also scavenges formaldehyde, which may be present in wood,particularly recycled wood. For applications such as plywood or veneerfor which higher viscosity is required, the second compound can beeither added or omitted, and the solids content of the dispersionincreased to increase its viscosity.

Biopolymer nanoparticles may be made with single biopolymers or withblends of biopolymers. For example, commercial EcoSphere® 2202nanoparticles available from EcoSynthetix and made from crosslinked waxycorn starch may be used. However, the addition of some potato starchprovides improved water resistance in the finished product. Other formsof starch, such as cold soluble starches (e.g., dextrins or otherchemically modified starches) or cooked chemically modified (e.g.,hydroxyethylated, hydroxypropylated) starches may also be used, but arenot preferred. In some trials, cold soluble starches were found toprovide acceptable performance only after they were first cooked or leftstanding for long periods of time, although better performance mighthave been obtained if the phase ratio of pMDI:Water had been higher whenthe isocyanate was added, and/or of the emulsion had been diluted afterthe isocyanate was added. Further, the viscosity of cooked or coldsoluble starch without pMDI may be acceptable for spraying, and resultswith nanoparticle starch applied separately from pMDI suggest thatapplying cooked starches generally (or thermoplastic melt phase starchproduced otherwise) or cold water soluble starch separately from pMDIwould produce an acceptable product. The preferred starch is, however, abiopolymer nanoparticle starch whichmore easily and reliably producesstable binders. The second compound may be dispersed, dissolved or mixedin an aqueous solution or dispersion of the biopolymer. Alternatively,the second compound can be incorporated with the biopolymer by addingthe second compound to an extruder (either before or after the reactionzone) used to make biopolymer nanoparticles. For example, waxy cornstarch or a mixture of waxy corn starch and potato starch can beextruded with urea. A less hydrophilic nanoparticle may be made of waxycorn starch extruded with 10 parts melamine and 5 parts citric acid.Incorporating biopolymer nanoparticles with a second compound viaextrusion may be useful, for example, to simplify mixing steps at theboard manufacturing site.

Binders preferably remain stable at normal operating process conditionssuch as temperature and dwell time prior to curing, maintaining boththeir low viscosity and reactive groups. Typical operating temperaturesrange from about 40-75° C., at time periods ranging from about 15minutes to about 1 hour or more. Binders that are stable for longerperiods of time are generally easier to use in manufacturing. To make awood composite, the biopolymer-isocyanate binder may be applied on woodchips, saw dust and/or fiber filaments which are at about 50-60 degreesC., maintained in an oven at about 70 degrees C. and then cured in apress at about 180 degrees C. Curing in the press may producetemperatures of 170-190° C. at the product surface but the temperatureat the core of the product could be between 100 to 120° C. The binder ispreferably able to cure at 110° C. or less but withstand 190° C. withoutdecomposing.

The biopolymer and isocyanate may be applied together, meaning that thebiopolymer and second compound (if any) are mixed with the isocyanatebefore being applied on wood chips before they pass through a dryer forMDF, or at the resonator for particle board. The spraying may be doneinto a “blow line” for MDF where wood chips pass through at about 50%moisture. In the dryer, the wood chips are dried to about 12% waterbefore being formed and pressed into boards. Alternatively, thebiopolymer and isocyanate may be applied “back to back”, meaning thatthe biopolymer and second compound (if any) are applied on wood chipsbefore they pass through a dryer first and then the isocyanate isseparately applied on wood chips but still before they pass through adryer. In another alternative, the biopolymer and isocyanate may beapplied “after dryer”, which is like back to back but the isocyanate isapplied on the wood chips after they pass through the dryer. The resultsare better in “together” application, but for some compounds that do notmix well, a “back to back” or “after dryer” application may bepreferred. “After dryer” application may be useful to avoid pMDIaccumulation on metal surfaces before the dryer. The physical propertiesof the resulting board appear to be best when the biopolymer andisocyanate are applied together, but “after dryer” isocyanateapplication provides useful products.

A binder may have various additives. Urea, mentioned above, is useful toreduce the viscosity of the binder, as a crosslinker and to scavengeformaldehyde released from the wood component. Although the binderpreferably has no added formaldehyde, some formaldehyde occurs naturallyin wood and composite products are often made from recycled woodproducts, which often contain formaldehyde. Other humectants, such ascalcium chloride or glycerol, may also be added to lower viscosity ofthe binder. One or more release agents may be added, although lessrelease agent is required than when using pMDI alone since thebiopolymer-isocyanate mixtures demonstrate reduced plate and beltsticking. Silicone containing products may be added to increase waterresistance of the finished product, and to act as a release agent.

The binders can be mixed in an in-line static mixer, for example of thetype having a set of fins inside of a segment of tube. Two inlets areprovided at the upstream end of the mixer. One inlet carries a mixtureof water, biopolymer and any urea or other additives. The second inletcarries pMDI. Mixed binder is produced at the downstream end of themixer. The downstream end of the mixer may be connected to a blowline orresonator, or other sprayer or addition system.

In an example of a mixing process, the biopolymer and urea, if any, aremixed into water under appropriate conditions. Cold soluble starch, forexample, may be mixed at 200 rpm using a mechanical prop mixer underrelatively low shear. Starch nanoparticles may be dispersed withrelatively high shear. The agitation speed may be about 400 rpm whilethe isocyanate is added slowly. Once all of the isocyanate is added,mixing continues for about 5 minutes until a homogenous emulsion isobserved. Optionally, the emulsion may be diluted by adding more waterwhile maintaining 400 rpm.

FIG. 1 provides an example of the initial RVA viscosity-phase ratiorelationship for pMDI (“oil”) in water emulsions at 40° C. in thepresence of starch nanoparticles in the following weight ratio samplecomposition (Biopolymer:Urea:pMDI:Water)=(21:4:75:water varies). Toprepare the samples, a biopolymer dispersion containing urea wasprepared using a mechanical prop mixer under relatively high shear. Therequired amount of this biopolymer dispersion was then added to anappropriate container for the RVA. The additional amounts of pMDI andwater, if any, were added. The components were emulsified at 40° C. for5 minutes at 500 rpm, followed by 5 minutes at 100 rpm. The viscosityreading was taken directly after the completion of the second 5 minutesof mixing.

The preferred window of operation, in relation to viscosity, is enclosedby a viscosity cut-off of 500 cP and a maximum phase ratio of about 1.5.As FIG. 1 demonstrates, with the appropriate water to pMDI ratio, abinder with a 25:75 ratio of biopolymer to pMDI can have viscosity thatmeets requirements of an MDF or particle board process. Acceptableviscosity can be produced when the weight of pMDI is not more than 150%,or preferably not more than 130% or 110% of the weight of water, andwhen the combined weight of biopolymer and pMDI is not more than 200% ofthe weight of water. However, as will be discussed below, the emulsioncan be prepared at a pMDI:Water phase ratio of over 1.5 and then dilutedto a phase ratio of 1.5 or less for application to wood. Such dilutioncan produce a more stable emulsion.

FIG. 2 illustrates light microscopy images of pMDI in water emulsions atdifferent pMDI:Water phase ratios (β) in the presence of starchnanoparticles in the following weight ratio sample composition(Biopolymer:Urea:pMDI:Water)=(21:4:75:water varies). FIG. 2 demonstratesthat at a ratio of β=1.6 more consistent and smaller droplet sizes arecreated. Smaller droplets have been found to result in emulsions thatare stable for a longer time period. In contrast, at β=0.8 much larger,less consistent and less stable droplets are formed. Although theseemulsions at β=0.8 or less may have a viscosity below 500 cP for 30minutes of more under constant mixing, there is macroscopic phaseseparation of these larger droplet emulsions on the time scale of a fewminutes once agitation is stopped. Although these emulsions may be usedif applied immediately after mixing, emulsions made with β=0.8 are morestable and more suitable for particle board and MDF processing.

In FIG. 3, a starch nanoparticle dispersion was prepared using amechanical prop mixer under relatively high shear. The agitation speedwas increased to 400 rpm and pMDI was added slowly. Once all of the pMDIhad been added to achieve a pMDI:Water phase ratio of 1.6, mixing wascontinued for 5 min until a homogenous emulsion was observed. The pMDIin water emulsion was then further diluted to a phase ratio of 1.0 byadding the required amount of water to the emulsion while maintaining400 rpm for 5 minutes. The Brookfield viscosity of the samples beforeand after addition of the water was measured using spindle #4 at 100 rpmand at room temperature.

FIG. 3 illustrates light microscopy images and image analysis resultsindicating that the emulsion with pMDI added to a phase ratio of 1.6 hasa relatively small and consistent droplet size. This emulsion is stableand does not phase separate even when left standing for extended periodsof time without mixing. While the viscosity of the emulsion at thisphase ratio would be too high, the viscosity was reduced by dilution toa phase ratio of 1.0 to meet the requirements of an MDF or particleboard making process. Of note, the particle size did not materiallychange during the dilution indicated that, during the 5 minutes ofmixing after the pMDI was added, a stable shell (as visible in FIGS. 2and 3) had already formed around the isocyanate droplets. It is possiblethat the shell already include starch-urethane reaction products.Dilution to a phase ratio of 1.0 produced a viscosity comparable to anemulsion produced by adding pMDI to an equal weight of water as recordedin FIG. 1. However, the average droplet size of 11.6 microns for theemulsion diluted to a phase ratio of 1.0 is at least an order ofmagnitude less than the droplet size that is produced when an emulsionis originally created at a phase ratio of 1.0. Further, the emulsiondiluted to a phase ratio of 1.0 is stable even when left withoutstirring. In contrast, emulsions initially made at a phase ratio of 1.0are less stable and will phase separate if left un-stirred. Thusviscosity is related to phase ratio at the time of the viscositymeasurement, but droplet size and un-stirred stability are related tothe phase ratio that was present when the pMDI was first added to thebiopolymer in water dispersion. The droplet size and un-stirredstability are related to the initial phase ratio that was present whenthe pMDI was first added to the biopolymer in water dispersion, theviscosity can be independently controlled through dilution of theemulsion. The smaller droplets are apparently more stable. Accordingly,it is preferred to make emulsions with a phase ratio of more than 0.8,preferably 1.0 or more, and to dilute the initial emulsion if a lowerviscosity or lower solids content is desired. While emulsions that areremain homogenous only during or directly after mixing are useful, morestable emulsions are preferred. The average isocyanate droplet size inan emulsion is preferably 500 microns or less, 250 microns or less, or100 microns or less.

FIG. 4 shows the evolution of RVA viscosity over time at 40° C. for apMDI in water emulsion over a 30 minute time period in the presence ofbiopolymer nanoparticles in the following weight ratio samplecomposition (Biopolymer:Urea:pMDI:Water)=(21:4:75:75). The viscosity wasmeasured in a rapid visco analyzer at 100 rpm, and indicates a stableemulsion within the target viscosity range.

Examples I. Biopolymer Samples

Various different biopolymer samples used in making binders aredescribed in Table 1 below. In the case of biopolymer nanoparticles,these were made by reactive extrusion generally as described inInternational Publication Number WO 2008/022127 (see Table 1).

TABLE 1 Summary of Biopolymer Samples Nanoparticle A (2202) CommercialEcoSphere ® biopolymer nanoparticles (crosslinked waxy corn starchnanoparticles extruded with 0 parts urea per 100 parts starch)Nanoparticle B (X250) biopolymer nanoparticles made of waxy corn starchextruded with 10 parts urea per 100 parts starch Nanoparticle C (X250P)biopolymer nanoparticles made of 75% waxy corn starch and 25% potatostarch extruded with 10 parts urea per 100 parts starch Nanoparticle D(X371) biopolymer nanoparticles made of 25% potato starch and 75% waxycorn starch extruded with a crosslinker and 0 parts urea per 100 partsstarch Nanoparticle E (X393) biopolymer nanoparticles made of waxy cornstarch extruded with 10 parts melamine and 5 parts citric acid per 100parts starch Cold soluble starch C*iCoat ™ produced by Cargill Cookedcold soluble starch Cooked C*iCoat ™ produced by Cargill Extruded starch(X3000) Waxy corn starch converted into a thermo- plastic melt phase inan extruder

II. Viscosity of Biopolymer Dispersions

Samples of biopolymers were dispersed in water at 30 wt % solids using asmall amount of sodium carbonate or sodium hydroxide to adjust the pH toabout 8, and secondly 5 wt % urea was dissolved to obtain 35% solidsdispersions. The viscosity of the samples was measured at roomtemperature (RT) using a DVII Brookfield Viscometer (spindle #5 at 200rpm). The results of the viscosity measurements are provided in Table 2.

TABLE 2 Viscosity of Biopolymer Dispersions Viscosity (cP) Viscosity(cP) Biopolymer Sample Without Urea With Urea X371 504 276 2202 776 280uncooked C*iCoat 800 528 cooked cold soluble starch 244 196 extrudedwaxy 4160 2600

As indicated in Table 2, urea had the effect of substantially reducingthe viscosity of all of the biopolymer dispersions.

III. Viscosity of Biopolymer/pMDI Dispersions

Samples of biopolymers, pMDI, urea (in some samples) and water wereprepared using the weights of each constituent given in Tables 3 to 7.The samples also contain a small amount of sodium carbonate or sodiumhydroxide to adjust the pH to about 8 and biocide at up to 0.1% of thetotal solids. The biopolymer and urea, if any, were first mixed into thewater at 200 rpm using a mechanical prop mixer under relatively lowshear. Mixing continued at 200 rpm while the pMDI was added slowly. Onceall of the pMDI had been added, the mixing speed was increased up to 700rpm until a homogenous emulsion was observed. The Brookfield viscosityof the samples was measured under similar conditions as listed above. Inaddition, the viscosity of some samples was also measured using a rapidvisco analyzer (RVA) maintained under isothermal conditions at 40° C.Stirring in the RVA for the first 5 minutes was at 500 rpm followed bystirring at 100 rpm for a further 25 minutes to make up the 30 minutetime noted in the Tables. The results of the viscosity measurements areprovided in Tables 3-7. The designation “N/A” in the following tablesindicates that a particular measurement of a particular sample was notcarried out, while designation “Gel” indicates the viscosity was toohigh to measure.

TABLE 3 Viscosity of X371 and pMDI Dispersions Initial BrookfieldBrookfield RVA Sample Composition (Bio- Brookfield Viscosity (cP)Viscosity (cP) Viscosity (cP) polymer:Urea:pMDI:Water) Viscosity (cP)after 30 minutes after 120 minutes after 30 minutes (g) at RT at RT atRT at 40° C. 25:0:75:45 3800 4900 18000 N/A 21:4:75:45 2300 3300 85001424  37:0:75:73 2200 3850 11800 N/A 31:6:75:73 1700 2200 4200 624 75:0:75:136 1248 1800 3000 N/A 63:12:75:136 820 1040 1200 362

TABLE 4 Viscosity of 2202 and pMDI Dispersions Initial BrookfieldBrookfield Sample Composition (Bio- Brookfield Viscosity (cP) Viscosity(cP) polymer:Urea:pMDI:Water) Viscosity (cP) after 30 minutes after 120minutes (g) at RT at RT at RT 25:0:75:45 5840 13600 Gel 21:4:75:45 36505880 Gel 37:0:75:73 3268 52100 37480  31:6:75:73 1422 1888 7390 75:0:75:136 1508 2096 8160 63:12:75:136 736 836 1280

TABLE 5 Viscosity of un-cooked cold soluble C*iCoat starch and pMDIDispersions Initial Brookfield Brookfield Sample Composition (Bio-Brookfield Viscosity (cP) Viscosity (cP) polymer:Urea:pMDI:Water)Viscosity (cP) after 30 minutes after 120 minutes (g) at RT at RT at RT25:0:75:45 4300 13860 Gel 21:4:75:45 5230 14240 Gel 37:0:75:73 305012180 Gel 31:6:75:73 2980 19920 Gel  75:0:75:136 3120 26160 Gel63:12:75:136 1756 16040 Gel

TABLE 6 Viscosity of cooked cold soluble C*iCoat starch and pMDIDispersions Initial Brookfield Brookfield Sample Composition (Bio-Brookfield Viscosity (cP) Viscosity (cP) polymer:Urea:pMDI:Water)Viscosity (cP) after 30 minutes after 120 minutes (g) at RT at RT at RT25:0:75:45 1352  2172  5380 21:4:75:45 756 1236  2260 37:0:75:73 N/A N/AN/A 31:6:75:73 N/A N/A N/A  75:0:75:136 420 472  632 63:12:75:136 338398  600

TABLE 7 Viscosity of X3000 extruded starch and pMDI Dispersions InitialBrookfield Brookfield Sample Composition (Bio- Brookfield Viscosity (cP)Viscosity (cP) polymer:Urea:pMDI:Water) Viscosity (cP) after 30 minutesafter 120 minutes (g) at RT at RT at RT 25:0:75:45 2060 3520 712021:4:75:45 1880 3280 6160 37:0:75:73 N/A N/A N/A 31:6:75:73 N/A N/A N/A 75:0:75:136 13040  39900  N/A 63:12:75:136 8210 39200  N/A

As indicated in Tables 3-7, binders using X371, 2202 and cooked coldsoluble starch were produced having a viscosity of about 1000 cP or lessat room temperature. These viscosities remained below about 1000 cP forat least 30 minutes. Given the results above for Brookfield viscosity atroom temperature (RT) and RVA viscosity at 40° C. it can be concludedthat the lower viscosity results for some of the formulations describedcan meet the viscosity requirements of an MDF or particle board process.

IV. Production of Particle Board in the Laboratory

Particle board samples at 18 mm thickness were produced as described inTable 8 at 3% overall binder loading. All test procedures are asdocumented in ASTM D1037-12. All dispersions were made at 35% solidsincluding 30% biopolymer and 5% urea. As the data in Table 8demonstrate, board properties are comparable for all formulations foreach substitution level.

TABLE 8 Comparison of the properties for lab-produced particle boardusing different biopolymers and pMDI Cooked Cooked C*iCoat/ X371/pMDI2202/pMDI C*iCoat/pMDI X371/pMDI 2202/pMDI pMDI 50:50 50:50 50:50 25:7525:75 25:75 pMDI Swelling 8.6 9.4 8.8 7.5 12.8 8.5 5.5 2 h (%) Swelling42.6 42.8 45.4 30.0 38.3 35.1 20.3 24 h (%) WA 2 h 37.1 52.3 44.2 33.358.7 47.6 27.9 (%) WA 24 h 111.6 122.6 123.1 89.9 115.8 106.8 67.5 (%)MOR 7.1 6.5 6.5 8.0 6.8 7.3 9.0 (MPa) MOE 1236 1064 1165 1338 1149 12761404 (MPa)

V. Curing Profiles of Biopolymer/pMDI Dispersions

Binders were prepared using 30% X371 plus 5% urea and two types of pMDIlabeled here as A (supplied by BASF) and B (MS300 supplied byElastochem) at two weight ratios. Onset, peak and endset curingtemperatures were determined by differential scanning calorimetry (DSC).The results are given in Table 9 below. All samples indicated curingprofiles suitable for use with existing wood composite manufacturingprocesses.

TABLE 9 Curing Temperature Curing Onset Curing Peak Curing EndsetTemperature Temperature Temperature Binder Composition (° C.) (° C.) (°C.) Biopolymer25 104 122 134 pMDI A 75 Biopolymer 50 100 116 130 pMDI A50 Biopolymer 25 109 120 132 pMDI B 75 Biopolymer 50 94 118 130 pMDI B50

VI. Industrial Scale Production of MDF

A binder was prepared having the following constituents: 25% ofX371/urea at an 85/15 ratio dispersed in water at a 35% total solids and75% pMDI sprayed separately.

Samples of 8 mm thick MDF flooring were made using a) pMDI applied at2.7% of the weight of wood and b) the pMDI/X371 mixture described aboveapplied at 2.7% of the weight of the wood based on the solids in themixture only. Results of tests on the samples are given below in Table10. As indicated, samples prepared with a 25% (1:3) replacement of pMDIwith X371 had performance comparable to samples produced with pMDIalone.

TABLE 10 Comparison of the properties for industrially- produced MDFboard using X371 biopolymer and pMDI pMDI 1:3 X371:pMDI Density 846 834MOR (N/mm²) 42.5 41.7 IB (N/mm²) 2.5 2.3 2 h TS 12.4 10.7 24 h TS 22.322.3 2 h WA 19.2 18.0 24 h WA 34.3 25.2

VII. Production of Particle Board in the Laboratory Using DifferentBiopolymers

Particle board samples at 18 mm thickness were produced as described inTable 11 at 5% overall binder loadings. All test procedures are asdocumented in ASTM D1037-12. All dispersions were made at 35% solidsusing different biopolymers as described in Table 1. As the data inTable 11 demonstrate, board properties can vary for differentformulations. The results demonstrate that Biopolymer A resulted in thebest board performance as compared to UF control board. As is commonpractice in the industry, the % solid binder loading=g of binder per 100g dry wood

TABLE 11 Comparison of the properties for lab-produced particle boardusing different biopolymers and pMDI Biopolymer Biopolymer BiopolymerBiopolymer Biopolymer UF A (4%), B (4%), C (4%), D (4%), E (4%), (10%)MS300 (1%) MS300 (1%) MS300 (1%) MS300 (1%) MS300 (1%) Swelling 24.517.8 32.1 30.3 16.9 13.3 2 h (%) Swelling 54.9 59.6 75.0 73.4 68.3 64.024 h (%) Average 11.1 15.3 12.3 11.7 15.4 12.8 MOR (MPa) Average 26432670 2108 2097 2564 2338 MOE (MPa)

VIII Alternative Addition Methods

All testing in this example is as per ASTM D1037-12.

The label “Together” indicates the biopolymer and isocyanate were mixedtogether and sprayed on the wood as a mixture before the dryer. Back toback indicates that the biopolymer dispersion was sprayed first and thepMDI was sprayed one minute later, but both before the dryer. Afterdryer indicates that the biopolymer dispersion was sprayed before thedryer and the pMDI was sprayed after the dryer. The biopolymer was X395(X371 with urea in an 85:15 mass ratio). The pMDI control was applied at3% (3 g pMDI per 100 g wood). In the “pMDI/X395 Together”, “pMDI/X395Back to Back” and “pMDI/X395 After Dryer” trials, X395 was applied at1.5% and pMDI was applied at 1.5%. The results are provided in Table 12below.

TABLE 12 Comparison of the properties for lab-produced particle boardusing different addition methods pMDI/X395 pMDI/X395 pMDI/X395 pMDITogether Back to Back After Dryer (3%) (3%) (3%) (3%) IB (MPa) 0.74 0.810.49 0.69 Swelling 8.0 8.2 12.1 9.5 2 h (%) Swelling 30.1 36.0 62.7 47.424 h (%) MOR (MPa) 13.9 15.8 11.4 14.6 MOE (MPa) 1987 2154 1846 2135

As indicated in Table 12, the Together application method demonstratescomparable performance to control pMDI. The Back to Back applicationresulted in board properties that were significantly worse thanapplication together or after the dryer. After Dryer application showedbetter results, but still without producing results comparable to pMDI.

IX. Production of Particle Board

Particle board samples at 10 mm thickness were produced as described inTable 13 at 3% overall binder loading. All test procedures are asdocumented in ASTM D1037-12. Dispersions of X395 were made at initiallyhigher solids contents and diluted down to 25% and 30% total solidsafter the pMDI was added. As the data in Table 13 demonstrate, boardproperties are comparable for formulations that were diluted to obtainlower RVA viscosity (below 300 cps) down to 25%, and further that 30%solids shows better results between the two final solids concentrationstested.

TABLE 13 Comparison of the properties for lab-produced particle boardusing different solids levels pMDI 25% pMDI 25% pMDI 35% pMDI 35% pMDI50% substitution, substitution, substitution, substitution,substitution, 30% solids 25% solids 30% solids 25% solids 25% solidsDescription pMDI X395 X395 X395 X395 X395 IB Average (MPa) 0.94 0.930.87 0.86 0.80 0.77 IB Std Deviation 0.10 0.06 0.10 0.06 0.07 0.08Density Average (Kg/m³) 670 674 672 682 671 676 Density Std Deviation 2418 16 24 23 38 2 h TS Average (%) 35.91 40.28 38.97 43.42 42.59 48.46 2h TS Std Deviation 1.91 2.00 3.03 1.75 2.19 3.59 Density Average (Kg/m³)686 683 686 678 680 687 Density Std Deviation 15 26 23 21 14 34 24 h TSAverage (%) 37.5 41.6 38.2 45.1 45.4 52.2 24 h TS Std Deviation 1.6 2.41.9 1.9 1.9 3.6 2 h WA Average (%) 80.0 85.9 84.7 92.8 92.6 95.3 2 h WAStd Deviation 2.3 2.7 3.6 3.8 2.7 3.5 24 h WA Average (%) 91.4 94.9 92.599.6 99.9 102.5 24 h WA Std Deviation 2.5 2.7 3.3 3.0 2.2 2.7 AverageMOR (MPa) 16.81 15.70 15.07 14.65 15.89 15.56 Average MOE (MPa) 23162241 2126 2211 2244 2223 Thickness (mm) 9.96 10.01 10.01 10.03 9.95 9.98

1. A composition comprising droplets in water, wherein the dropletscomprise one or more isocyanates and have an average droplet size of 500microns or less, and the droplets have shells comprising one or morebiopolymers or a reaction product of a biopolymer and isocyanate.
 2. Thecomposition of claim 1, wherein the one or more biopolymers comprisestarch with a molecular weight of 1,000,000 Da or less.
 3. Thecomposition of claim 1, wherein the one or more biopolymers comprisestarch nanoparticles.
 4. The composition of claim 1 wherein the mass ofthe one or more isocyanates is between 50% and 150% of the mass ofwater.
 5. The composition of claim 1 further comprising urea.
 6. Thecomposition of claim 1 wherein the mass ratio of the one or morebiopolymers to the one or more isocyanates is in the range of 15:85 to50:50.
 7. The composition of claim 1 comprising nanoparticles, wherein80% or more of the nanoparticles is made up of starch.
 8. Thecomposition of claim 1 wherein the one or more biopolymers is a mixtureof potato starch and corn starch.
 9. The composition of claim 1 whereinthe mass of the one or more isocyanates is not more than 130% or 110% ofthe mass of water.
 10. The composition of claim 1 wherein the mass ofone or more biopolymers is not more than 55% of the mass of water. 11.The composition of claim 1 having a viscosity of 500 cPs or less at 40°C.
 12. The composition of claim 1 further comprising wood. 13.(canceled)
 14. A method of making a binder comprising the steps ofmixing at least one biopolymer and water and adding at least oneisocyanate to the mixture, wherein the at least one biopolymer comprisesmodified starch selected from the group consisting of biopolymernanoparticle starch and starch having a molecular weight of 1,000,000 Daor less.
 15. The method of claim 14 wherein the at least one biopolymerand water mixture and the at least one isocyanate are fed separately toan in-line static mixer.
 16. The method of claim 14 further comprising astep of adding additional water.
 17. (canceled)
 18. (canceled) 19.(canceled)
 20. A composition comprising isocyanate, water, and starch,wherein the starch is selected from the group of starch nanoparticlesand modified starch having a molecular weight of 1,000,000 Da or less.21. The composition of claim 20 further comprising wood.
 22. Thecomposition of claim 21 wherein the starch and isocyanate have a weightbetween 2% and 8% of the weight of the wood.